Compass control indicator system



- April 18, 1944.

w. P. LEAR COMPASS CONTROL INDICATOR SYSTEM 2 Sheets-Sheet 1 Filed May15, 1943 2J- REMOTE NDICATORS T 70 INVENTOR. W/ZZ/A fl/ f. 154/? BY 2ATTORNEY April 18, 1944. w. LEAR 2,346,849

- COMPASS CONTROL INDICATOR SYSTEM Filed May 15, 1943 2 Sheets-Sheet 2ENE/W INV ENT OR. W! [/4/4 P. [AW/i ATTORNEY Patented Apr. 18 1944UNITED STATES PATENT OFFICE COMPASS CONTROL INDICATOR SYSTEM William P.Lear, Piqua, Ohio, assignor to Lear Avia, Inc., Piqua, Ohio, acorporation of 1111- nois Application May 15, 1943, Serial No. 431,074 419 Claims.

. from the instrument panel and pilot so as to avoid indication erorrsdue to the surrounding metallic structure. The compass indications are,furthermore, upset during maneuvering and aerobatics of the aircraftthat cause temporary spinning and turning errors on the magnetic compassneedle indications. The present invention is directed towards adirectional compass system wherein the indications are substantiallystable during aircraft maneuvers. Towards this end a directionalgyroscope is electronically related with the magnetic compass in amanner to stabilize the resultant bearing indications.

In accordance with the present invention I provide a simple, reliableand effective stabilized directional compass system. The magneticcompass is merely electrically coupled to the system. A standard compassis employed, which may be placed anywhere on the aircraft so as to berelatively unaffected by the metallic structure and armor. Spinning orturning reactions in'the magnetic compass are averaged out in the systemand do not erroneously effect the resultant indications. The directionalgyroscope is inherentlyflazy and stable over short periods of time, andthe composite effect with the mag- .netic compass is to affordstabilized directional indications that have an overall accuraterelationship to true magnetic north.

An important feature of the present invention is the substantiallytorqueless pick-off of both the navigator, bombardier, and othersthereon may have continuous, direct and stable bearing indications. 1The compass directional systems of the prior art provided only a limitednumber of remote indicators. An important aspect of the system of mypresent invention is the provision of any number of remote compassindicators. These indicators are actuated by locally generatedelectronic control currents. They are selfaligning, and correspond withthe direction of the stabilized directional readings. The remote compassindications are substantially unaffected by gyrations to which themagnetic compass may be temporarily subjected, or precessional errorswhich the directional gyroscope may tend to accumulate. Thus continuousaccurate compass bearings are simultaneously provided throughout theaircraft, without loading or otherwise reflecting errors back onto thecompass units.

A further important feature of the present invention is the provision ofa pick-oil unit in which the inertia of the rotor is greatly reduced bymechanically separating the rotor and the rotor winding.

Still another feature of the invention is the provision of improvedmeans for adjusting the sensitivity, of the control action of themagnetic compass on the directional gyroscope and improved means foradjusting the rate of corrective precessional movement of the gyroscope.

These and further advantages, objects, and

capabilities of my present invention will become more apparent in thefollowing description of a preferred embodiment thereof, shown in theaccompanying drawings, in which:

Fig. 1 is a diagrammatic representation of Fig. 2 is an enlargedsectional view of the pick-oi! unit associated with the directional gyvroscope.

magnetic and gyroscope compass bearings for effecting the orientationcontrol on the gyroscope. In prior systems, errors were introduced inthe resultant readings of the system due to the nature and arrangementsof the pick-off devices employed. The precessional errors-which thedirectional gyroscope slowly tends to accumulate during flight arecontinuously and automatically corrected with the magnetic compass as areference through the inter-coupled electronic control unit of theinvention. This system is referred to. as a northerly seekingdirectional gyroscope. Both the magnetic compass and directionalgyroscope used are of standard size, and conventional design andconstruction,

as are the other components of my system.

Large modern military aircraft generally require a number of remotecompass indications throughout the aircraft, so that the copilot,

' pick-off unit.

Fig. 3 is a schematic electrical diagram, of the Fig. 4 is a schematicelectrical diagram of a directional gyroscope and its associatedpick-off unit.

Fig. 5 is a schematic electrical diagram of a modified arrangement forthe pick-off unit.

Fig. dis a schematic electrical diagram of one embodiment whichmyinvention may assume in practice. I 7

Referring to the drawings, it will be noted that the essentialcomponents of the invention system are a directional gyroscope 10, amagnetic compass IS, an intercoupled electronic direction control unit20, and remote indicators 25 and 26. The system is energized by a localalternating current source II that is generally present aboard anaircraft. A 400cycle supply is indicated, although another frequency maybe used.

' by leads 2! and 28, respectively.

the pick-off unit connected with the directional gyroscope la isenergized from the source" ||,-J I while the stator windings of thepick-off units are symmetrically interconnected electrically. Thepick-off unit associated with the directional gyroscope thus correspondsto a transmitter element of a self-synchronous type of telemeteringarrangement. The pick-oil units associated with the magnetic compass l5and the remote indicators 25 and 26 correspond to receiver elements ofsuch self-synchronous type of telemetering arrangement.

Briefly speaking, in the event the rotors of the gyroscope l and themagnetic compass l are out of their predetermined directional alignment,the pick-off unit on the magnetic compass will be effective to actuatethe-directional control unit 20 which will effect a precessionalcorrection movement on the gyroscope rotor to restore the gyro scopecompass to its predetermined directional alignment. The remoteindicators are coupled to the gyroscope to repeat its readings throughthe association of the respective pick-off units. Means are provided fortesting and adjusting the sensitivity 'of the control action exerted bythe compass on the gyroscope, and other means are provided to adjust therate of corrective precessional movement of the gyroscope. Theconnections of the gyroscope and the compass to their pick-oil units aresubstantially torqueless, and the corrective mechanism of the remoteindicators is independently locally energized, so that substantially notorque is. exerted on the rotors of the gyroscope or magnetic compass.This assures accurate directional alignment of the gyroscope compass andremote indicators as the corrective action is accomplished withnegligible drag or torque which might interfere with accuratedirectional alignment. As will be apparent as the description proceeds,any number of remote bearing indicators .may be incorporated withoutintroducing drag on either the gyroscope in or the compass l5, since theindicators are locally energized and self-aligning.

The directional gyroscope I0 is of the conventional type, comprising arotor |2 mounted with three degrees of freedom, and which may beelectrically or pneumatically driven a will be understood by thoseskilled in the art. The gyro unit 20 from the magnetic compass IS, in amanner to be described hereinafter, generates a control current at theoutput of the unit 20 which is selectively applied to the windings 22and 23 through the leads21 and 28 respectively. The unidirectionalcorrective flux selectively produced in the windings 22 and 23 reactswith permanent magnets 29, 29 secured to the horizontal gimbal ring I3.The corrective force thus exerted on the magnets 29 is in a direction soas to counteract any precessional or turning errors that the gyroscopemight tend to incur. In this manner, and as will be more apparenthereinafter, the orientation and indications of the gyroscope are madestable, and tied to the true magnetic north indications of the magneticcompass |5.

A gyroscope bearing pick-off unit 30 is supported on a plate 3| thatismounted on top of the casing 2|. Pick-ofl. unit 30 comprises a centralvertical shaft 32 that is secured to the vertical ring I6 of thegyroscope. The directional position of the gyroscope is in this mannerdirectly communicated to unit 30. The shaft 32 and a second shaft 33form pivots for a hollow soft iron shaft 34 secured thereto and carryingtwo vanes 35 and 36. The pivot shafts 32 and 33 are supported in jewelbearings 81 and 33. The unit 30 includes a soft iron cylindrical outershell 39 in magnetic circuit with a metal core 40, formed toprovidebearing mountings for the shaft 34 and to permit rotation of thevanes 35 and 36. The shell 39 also serves as a magnetic shield for unit30.

A fixed rotor winding or rotor energizing coil 4| is mounted centrallyon the core 40 and, as

' shown in Figs. 2, 3 and 4, two stator windings rotor I2 is spun abouta horizontal spinning axis 5 supported in a gimbal ring l3, which inturn is freely mounted on bearings l4 in vertical ring IS. The verticalring I6 is rotatably supported about a vertical axis on bearings I! ofthe gyroscope, and a circular directional scale I3 is supported on thevertical ring l6, and viewed through a window l9 in the gyroscope casing2|. 1

The gyro indication correspond to the reading of scale I8 opposite theusual index 'or lubber line within the casing 2|, and concentricabouthori- ,zontal gimbal ring l3. The windings 22 and 23 are connectedto the directional control unit 20 The control signal introduced intothe directional control magnetic compass 42 and 43 are also mounted onthe core 40. The windings 42, 43 are spaced 90 electrical degrees apartand constitute a two-phase stator circuit.

'Rotor winding 4| is energized with single-phase alternating currentfrom source through leads 44. Leads 45 connect the stator windings 42,43 symmetrically to corresponding stator windings in identical pick-offunits associated with the H) and remote indicators 25, 26.

When the winding 4| of pick ofl unit 30 is energized with alternatingcurrent from source II, a magnetic flux is induced in the center. of therotor 34 and transmitted to the vanes 35 and 38, the magnetic circuitbeing completed by the shell 39. If the shaft assembly or rotor 34 ofthe unit 30 is rotated, the correspondinginduced magnetic field is alsorotated, inducing an E. M. F.

in the stator windings 42 and 43, the voltage in each phase beingdetermined by the geometric alignment of the rotor 34 and vanes 35 and36 with respect to the stator windings, The-voltages thus induced giverise to proportional alternating currents which flow in both the statorwindings and rotor, windings of the corresponding pick-off unitsassociated with magnetic compass l5 and remote indicators 25, 26, Thesealtemating currents set up a flux pattern in the receiver pick-off unitsidentical to the pattern in the transmitter pick-ofl unit 30. The fluxin each receiver unit reacts with the vanes thereof causing the receiverunit rotors to assume the same angular position as that of thetransmitting unit.

The transmitter pick-off unit 30 and the corresponding receiver pick-offunits associated with the magnetic compass I5 and the remote indicatorunits 25, 26 can be replaced by the pick-off units shown and describedin my above-mentioned copending application serial No. 454,559.

filed August 12, 1942. Such pick-ofi unit is shown diagrammatically inFig. and comprises a rotor shaft 46, which may be connected to theassociated gyroscope, magnetic compass or indicator unit. A rotorwinding 57 on rotorshaft it may be energized from local alternatingcurrent source il through leads 86'. The unit includes three statorwindings d8, 49, 50 connected in threephase delta arrangement, thesewindings being spaced 120 electrical degrees apart. Windings 4t, 89 and50 may be connected symmetrically to the stator windings of othersimilar pick-off units through leads 45'.

The magnetic compass is is of standard size and the conventional designgenerally used aboard an aircraft. It is a master magnetic compass,containing a substantial magnetic bar 5| which is mounted for freemovement in azimuth for alignment with the earth's magnetic field. Barmagnet 5| is within a float 52 which is pivotally supported within afluid 53 in the housing alignment with the magnetic bar 5|. The controlof the compass I5. A pivot spindle 54 is secured to float 52 andsupports the float and magnet bar 5| on a jewel bearing 55. A spring 56supports bearing 55 and also float 52 in a resilient manner. Magnet bar5| is thus freely supported for alignment with the earth's magneticfield, fluid 53 serving to dampen the movement of the magnet as wellasrelieve the pivot pressure on bearing 55.

A directional pick-oil unit 60 identical in construction with the unit30, is mounted on the casing of compass l5 and the directionalorientations of magnet bar 5| are communicated to the pickoff unit 60,as follows. A small magnet bar BI is mounted at the upper end of spindle54 and a second magnet 62 is mounted above magnet 5| and serves as afollow-up or slave magnet. Magnet 62 is connected to the rotor ofpick-off unit 50 through shaft 63. The azimuthal bearing indications ofthe main compass bar 5| are thus faithfully communicated to the rotor ofpick-oil unit 60. Such action is with the application of negligible dragor torque which might interfere with accurate directional alignment ofmagnet bar 5|. The stator windings of the unit 60 are symmetricallyinterconnected electrically with the stator windings of the unit 30through leads 45.

In the event the rotor l2 of gyroscope I0 is rotated out of alignmentwith the magnetic bar 5| of compass IS, the induced magnetic field inthe stator windings of unit 30 will be rotated, inducing an alternatingvoltages therein. These induced voltages give rise to proportionalcurrents which flow in the stator windings of both units 30 and 50,setting up a flux pattern in unit 50 identical to the pattern in unit30, and that reacts with its rotor vanes. The flux within the statorwinding of unit 50 is sinusoidal in time and induces a correspondingsinusoidal voltage in the The magnitude of the voltage across therotorwinding is proportional to the sine of the angle which the rotormakes with its zero pick-up position in the flux in the stator winding.

. The voltage induced in the rotor winding of unit 60 provides a controlsignal which is inipressed, through leads 61, upon the directionalsignal impressed upon unit is of a magnitude directly dependent upon theangular diiference that exists between bearings of the gyroscope It! andmagnetic compass l5, and of phase that is directly dependent upon thesense of theangular difference. The larger such angular difference, thegreater is the magnitude of the control signal impressed upon thedirectional control unit 20.

Thus, .in .practice, the orientation or bearing positions of gyroscopeH] are tied to or otherwise made to correspond with the azimuthalbearing position of compass l5. Both readings are made to refer totruemagnetic north as the reference, with the magnetic compass findingsuch north and the gyroscope being made to assome and maintain suchspatial reference. The

magnetic compass bar 5| naturally assumes such north position, orotherwise averages out its gyrations to effective north position.

The remote indicators 25, 25 include pickofi units identical with theunit 30. The stator windings of these pick-off units are symmetricallyinterconnected electrically with the stator windings of units 30 and 60through leads 45 and 70. In a manner to be described more particularlyhereinafter, the directional indications of the remote indicator units25, 26 are tied to the azimuthal bearing indications of gyroscope l0 andmagnetic compass l5.

The operation of the system in detail will be understood more clearlyby'reference to Fig. 6 which is a schematic wiring diagram of thesystem, including gyroscope l0, magnetic compass |5, a remote indicator25, and associated pick-off units. The pick-oil unit 50 associated withmagnetic compass |5 includes a rotor coupled to shaft 63, a fixed rotorwinding 12, and two-phase stator windings 13, ",arranged 90 electricaldegreesapart. Rotor winding H is connectedby leads 51 to directionalcontrol unit 20. Stator windings l3, 14 are symmetrically interconnectedelectrically with stator windings 42, 43 of gyroscope pick-on unit 30through leads 45.

The remote indicator 25 comprises a pick-oil unit 75 similar to units 30and 60 and including a fixed rotor winding 16, two-phase stator windingsl1 and I8 arranged 90 electrical degrees apart, and a rotor 80. RotorBllis mechanically coupled with an indicator needle or pointer 8|cooperating with an indicating scale 82. In order to maintain alignmentof remote indicator 25 with gyroscope Ill and compass I5, a motor 83 isprovided which has an armature :84 connected through gearing 85 to therotor 80. The

motor 83 also includes field windings 8G and 81 arranged electricaldegrees apart. The windings 88 and 81 are adapted to be energized torotate'the pointer 8| back into its pre determined directional alignmentwith gyroscope l0 and compass l5. s

' riod of time.

It will be noted that corresponding points on the stator windings of theunits 30, 60 and I5 are interconnected by leads 45. The localalterwinding SI of the transformer is impressed through a phasingresistor 92, a phasing con-,

denser 93, and leads 44 across the rotor winding H. of the gyroscopepick-oil! unit 30. Due to the symmetrical electrical interconnection ofthe stator windings of the several pick-ofi-units 30,

60 and I5 and to the transformer action between the stator windings andthe rotor windings of these units, the same phasing voltage will be.impressed upon the rotor winding "I2 of magnetic-compass unit and therotor wind-' ing I of the remote indicator unit I5.

In practice, the orientation or bearing positions of gyroscope I0 aretied to" or otherwise made to correspond with the azimuthal bearingpositions of magnetic compass I5. Both readings are thus made to referto magnetic north as a reference. The magnetic compass I5 finds suchnorth and the gyroscope I0 is made to assume and maintain; such spatialreference. The magnetic compass I5 is more sensitive to aerobaticdisturbances due to the aircraft, but its northerly indications averageout over a pe- In straight flight, its indications are quite stable. 0nthe other hand, gyroscope I0, having three degrees of freedom Is arelatively stable indicator. Its northerly turning or precessionalerrors are cumulative only over a substantial period of time amountingto at least several minutes. The precessional control action of compassI5 on gyroscope through'control unit- 20 and coils 22 and 23 is made tobe only slowly errors, since such errors are automatically eliminated byreference to and control by the average northerly readings'of magneticcompass I5.

The single phase voltage applied to rotor winding4I through leads 44produces a sinusoidal magnetic field that. induces voltages in statorwindings 4'2, 43. The relative phase and magnitude of the inducedvoltages in each stator winding depend upon the angular position ofrotor 34 within windings H, 42 and 43. Such angular position is in turncontrolled by the directional orientation of gyroscope I0 throughvertical ring IS. The induced voltages appearing at the terminals ofwindings 42, 43 are transmitted through leads 45 t0 the correspond ingterminals of stator windings I3, I4 of compass unit-60. There, theyproduce alternating currents in windings 13, I4 corresponding to thosein windings 42, 43. A magnetic field is thus set up in windings 13, I4that is identical in space and time relationship with that .withinstator windings 42, 43 as controlled by the position of rotor 34. Theflux within stator windings I3, I4 is sinusoidal in time. This flux in-'duces a corresponding sinusoidal voltage in rotor winding 12 of compassunit 60.

. The magnitude and phase of the voltage .produced across rotor coil I2depends on the angular space phase of rotor II within coils I2, 'I3'and.14. The resultant voltage in rotor coil I2 is inphase or 180.outot-phase with the magnetic aseasee flux of stator windings 13, id.The magnitude of the resultant voltage in rotor coil I2 is proportionalto the sine of the angle which rotor H makes with its zero pick-upposition in coils I2, I3 and I4, and the magnitude and phase of thevgltages induced in coils I3, I4 by gyroscope unit 31 The voltageinduced in rotor coil E2 is impressed, across phasing and by-passcondenser 05, upon the grid 96 of a dual electronic tube 01. The inducedvoltage is amplified and impressed through plate 98 and couplingcondenser Q00 upon the controlgrid IIII of the second amplifier sectionin cascade. The cathode bias. of tube 9I is controlled by resistor I02and condenser I03.

From plate I04 of tube 91, the amplified voltage from rotor coil 12 isimpressed, in phase.

through coupling condenser I05 and grid leak resistances I06, I01, uponthe grids I08, I09 of control tubes IIO, III. Tubes H0 and III may begas filled tubes, such as thyratron tubes, which act as electric valvespermitting full flow of current when the grid potential is raised abovea critical value. A requisite higher alternating voltage of the samelocal frequency as that applied to grids I08, I09, is impressed on theplates H2, H3 of tubes IIO, III from local source II through thesecondary winding II4 of trans- .former 90. The circuit for impressingthisialtemating voltage on plates I I2, I I3 includes leads 68,gyroscope precession windings 22, 23, leads II5, limiting resistor banksH1, H8 ganged at H6, and leads I20. It will be noted that theconnections are such that plates H2, H3 are 180 out of phase with eachother. Depending upon which one of plates I I2, II 3 is in phase withthe alternating voltageapplied to grids I08, I09. oneOr the other oftubes H0 or III will become conductive allowing the current to flowthrough the associated gyro precessional coil 22 or 23.

Energization of coil 22 or coil 23 will influence magnets 29, 29 andprecess gyro rotor I2 toward the null point or the point at which gyrorotor I2 and magnet bar 5| of compass I5 are in directional alignment.When such directional alignment is attained, no control or signalvoltage will'be' applied to grid 98 of tube 91, and thyratrons IIO, IIIwill cease to fire, and have no further efiect on the precession of thegyroscope. The gyroscope I 0 will at such time be in alignment with themagnetic compass I5.

The sensitivity of tubes 0, III, and thus the sensitivity of theprecessional action on gyroscope I0, is controllable by the adjustablegrid biasing resistor I25 connected across a suitable of precession ofgyroscope I0. The rate of pro-- cession is determined prior toinstallation of the apparatus and isset with a proper sensitivitycontrol of resistor I25. The adjustment of resistor I25 will bedescribed in detail later.

It ha been found, in practice, thatthe voltages normally from pick-oflunits 30 and 80 do not have a perfect or sharp null point. On Ior nearthe null, a spurious unwanted 90 voltage comes from the pick-off units,probably due to the 90 relation of the stator windings in the de scribedunits. This spurious voltage tends to reduce the selectivityof'thyratrons IIO and-III. The consequence is that both thyratron willfire together. To overcome this condition, a direct current negativevoltage or bias is obtained from tube I I by applying resistors I28 andI30 between the plate II2 and ground. At the Junction I3I of resistorsI28 and I30, this direct current negative voltage is taken off andfiltered through resistor I32 and condenser I33. At the junction I34 ofresistor I32 and condenser I33, an appreciable suitable D. C. negativevoltage is ob.- tained and applied through resistor I35 to grid I08 oithyratron III. duction of this direct negative potential, as soon asthyratron IIO fires, it becomes harder for thyratron III to fire.However, as grid I09 of thyratron III is thus desensitized, thyratronIIO has a tendency to continue firing as the null is approached. Toovercome this latter tendency, a portion of the negative voltage frompoint I34 is fed through a resistor I38 to grid I08 of thyratron IIO.Therefore, assoon as thyratron IIO fires, its own-grid I08 is alsodesensitized. This action has little, if any, effect upon thecontinuation of firing of thyratron IIO, but, as soon as a null isreached, it promptly ceases to fire. The practical conditions is thusobtained in which either thyraton H0 or thyratron III fires im mediatelyon each side of the null.

In order to obtain the proper sensitivity of the apparatus, it isdesirable that thyratron IIO fire at a full rate immediately upon anangular deviation between units 30 and 60. To obtain this condition, aresistor I31 is connected between cathode I38 of thyratron H0 andground. By the introduction of resistor I31, as soon as thyratron I I0fires there is a positive voltage between cathode I38 and ground. If theshield I40 of thyra-' tron IIO is then connected to cathode I 38, thepositive voltage on the shield will accelerate the firing of tube H0 andalmost immediately it will fire at its full rated current.

With the above described arrangement, the

back is introduced between plates 98, I04 of am plifier tube 91 byconnecting resistor I4I between such plates. This resistor also helps toeliminate the aforementioned spurious 90 voltage and sharpens thecontrol action of thyratrons III) and III. With proper adjustment,thyratrons H0 and III can be made to fire with a directional variationof less than a degree, and with deviations of less than A, of a degreeon either side of the null or bearing point.

To determine the adjustment of grid biasing resistor I25 for the desiredsetting of sensitivity control of thyratrons IIII, III, it is generallynecessary to use an external meter. For this reason, jacks I42 and I43are connected between the cathodes of thyratrons IIO, III and ground.These jacks allow the plugging in of varying amounts of resistance andmeter con; nections with which the proper adjustment of the sensitivityof grid biasing resistor I25 for the grids of tubes IIO, III can bedetermined.

Once the proper adjustment of resistor I25 is determined, theresistances are removed and the adjustment of resistor I25 is locked inplace.

Thus, due to the intro- In the event there is a change in the azimuthalbearing of thagyroscope I0, due to control action by magnetic compassI5, pointer 8I of remote indicator 25 will be out of its predetermineddirectional alignment with vertical ring I6 to' gyroscope l0. Rotor 80of remote indicator pickofi unit will thus be out of predetermineddirectional alignment with rotor 34 of gyroscope 5 netic flux producedin stator windings 11, 18.

The magnitude of the voltage in rotor coil 16 will be proportional tothe sine of the angle which rotor 80 makes with its zero pick-upposition in coils 16, 11, 18.

The alternating control voltage developed I 4 across the rotor winding16 is applied, through leads I45 and across phasing and by-pass con=denser I46, to the control grid I41 of an electronic amplifier I48. Anadjustable bias for adjusting the sensitivity of tube I48 is provided bya potentiometer I50 connected in parallel with a battery or othersuitable source of direct current I5I. A by-pass condenser I52 is inparallel with potentiometer I50. The alternating .voltage or signal thusapplied to grid I41 of tube I48 is amplified in class A, and applied inphase, through coupling condenser I53, to the grids I54 and I55 of adual electronic tube. I56. To control the sensitivity of tube I56,an'adjustable bias for grids I54 and I55 is provided by a potentiometerI51 connected in parallel with a battery or other source of directcurrent I58.

A requisite higher voltage of the same local frequency as the controlvoltage impressed on grids I54, I55 of tube I56 is impressed on platesI60, IIiI of the tube from secondary winding I14 of transformer 90. Thisvoltage is impressed on plates I60, I6I from leads 68 through theprimary windings I62, I63 of saturable core reactors I64, I65.Condensers I66, I61 connected in parallel with windings I82, I63 improvethe performance of the control action.

The motor 83 which is back geared to the re-v mote indicator pointer Mis of the quarter or split-phase type, in which the respective voltagesapplied to windings 86, 81 are electrical degrees out-of-phase. For thispurpose, a voltage from secondary winding II4 is-impressed directly onwinding 86 through leads 68. Thevoltage for winding 81 is selectivelyimpressed thereon from leads 68 through secondary winding I68 or I69 ofreactors I64, I65. To provide the requisite 90 displacement of thevoltage across winding 81 with respect to that across winding 86, acondenser I10 is connected in the lead "I extending between the windingsI68, I69 and winding 81.

The aforementioned alternating current control voltage from the rotorwinding 16 is impressed through tube I 48 in phase on grids I54, I55 oftube I56. Plates I60, I6I are'connected to opposite terminals ofsecondary winding II4 of transformer 90, so that the voltages applied tothese plates are out-of-phase with each other. Accordingly, one or theother ofplates I60, "II will become conductivedepending upon which plateis in phase with the grids I54, I55. The resulting current flowingthrough one of the windings I62, I63 will saturate the core of itsrespective reactor I64 or I65. Such saturation makes negligible thealternating current im-, pedance of the associated secondary winding I68or I69. With the normally high impedance of the saturable reactor thussubstantially reduced, voltage from secondary winding 4 of transformer98 will be applied through condenser I18 to the winding 81 of motor 83.Depending upon which section of tube I56 fires, the voltage applied towinding 81 will lead or lag that applied to winding 86 by 90. In effect,windings 86, 81 comprises a reversible two-phase field for motor 83.

As previously explained, armature 84 of motor 83 is back geared throughgearing 85 'to the rotor 80 of pick-off unit 15, and to the pointer 8|of remote indicator 25. The motor 83 will turn rotor 80 and pointer 8|until the rotor is in directional alignment with rotor 34 ofgyroscopepick-oil unit 38 and pointer 8| has the predetermined directional'alignmentwith the vertical ring I6 of gyroscope III. When rotor 80reaches its point of zero flux pick-up in windings 16, 11, 18, whichpoint corresponds to predetermined directional alignment between rotors80 and 34, no alternating control voltage will be applied to grid I41 oftube I48, and consequently there will be no activating voltage appliedto grids I54, I55 of tube I56. Accordingly, reactors I64, I65, willbecome effective to block cur-' rent from winding 81 and stop motor 83.The remote indicator 25 is thus inductively coupled to and controlled bygyroscope I and gives accurate indication of the bearing of gyroscopeIII as such bearing is corrected by reference to the bearing of magneticcompass I 5.

As the control circuits include inductances, such as the windings of thepick-off units 30, 68 and 15, the control signal applied to the controlgrids of tubes H8, III and I 56 from reference source II through rotorwinding 4| and the pickofi unitsmay in practice not be exactly in-phaseor exactly 180 out-of-phase with the voltage applied from the referencesource II to the plates of these tubes. Towards this end condensers 93,95 and I46 are provided to counterbalance the eilect of the circuitinductances to the extent necessary to bring the grid voltage of tubesIIO,

, of gyroscope I 0 and compass I5 an alternating control voltage of amagnitude proportional to such angular deviation and a relative phasedependent upon the directional sense of the deviation is impressed onthe grid 86 of the tube 81. Depending upon which side of the null orbalance point such deviation takes place, either tube IIO or tube IIIwill fire permitting one of the coils 22 or 23 to be energized. Theenergized coil will influence the magnets 29 to precess the gyro rotorI2 in a direction to correct the deviation. As soon as the null point ofrotor 1| with respect to rotor 34 has been reattained, there will be novoltage impressed on the grid 98, and the tubes 1 I 0 and III will notfire. At the same time, if there is a deviation between the pick-offunit rotor of any remote indicator and the rotor 34mm alternatingcontrol voltage will be impressed upon grid I41 of the tube I48, whichtube will amplify such voltage and impress it, in-phase, on the gridsI54 and I55 of the tube I56. One or the other of the plates I60 or I6Iwill become conductive, depending upon which one is in phase with theimpressed grid voltage, neutralizing the reactance in the correspondingone of the saturable reactors I64 or I 65. Current from the transformerwinding I I4 will then fiowthrough the windings of the motor 10 in thephase relation causing the same to restore the alignment between rotor88 and rotor 34. When such alignment is restored, no voltage will beimpressed on grid I41 and the motor will be deenergized.

Thus, the gyroscope III is tied to the magnetic compass I5 so that itbecomes a northerly seeking gyroscope. The gyroscope inherently tends toremain fairly stable over a period of time, whereas the magnetic compassmay vary widely due to aerobatics of the plane. However, suchvariationsof the magnetic compass are averaged out over a period oftime, so that, on the average the indications of the gyroscope arewithin less than one degree of the northerly indications of the magneticcompass.

Similarly, the beamings of remote indicators and 26 are tied to thebearings of gyroscope I 0 and magnetic compass I5 so that these remoteindicators closely follow the movements'.of the gyroscope and compass.As the remote indicators are energized locally, they exert substantiallyno torque upon the gyroscope and the magnetic compass. The torqueexerted upon all of the units is further reduced by the separation ofthe rotor windings of the pick-off units from the rotors thereof, and bythe provision of the slave magnet 62 for picking off the indications ofthe compass I5. Thus, the whole compass system is very sensitive andaccurate in its operation, as substantially no errors are .introduceddue "to torque or drag upon the gyroscope I0 or the compass I5.

Furthermore, the several described circuit-s provided for an accurateadjustment and setting of the sensitivity of the telemeteringarrangement between the gyroscope and the compass, and between thegyroscope and the remote indicators. Means are provided also foradjustment of the desired rate of precession of the gyroscope. While theapparatus has been illustrated in Fig. 6 as including only the remoteindicator unit 25, it should be understood that as many remoteindicators may be included as are necessary or desirable, and that thenumber of such indicators will have no effect upon the accuracy of thegyroscope and compass indications, due to the fact that the indicatorsare energized locally and thus exert substantially no torque upon thegyroscope and compass.

While specific embodiments of the invention have been selected for thepurpose of illustration, it will be understood to those skilled in theart that the invention may be otherwise embodied without departing fromthe principles thereof.

What is claimed is:

1. A compass system comprising a gyroscope; a first rotor coupled tosaid gyroscope and oriented thereby in correspondence with thedirectional position thereof; a first rotor winding magnetically coupledto said rotor; a first stator winding in inductive relation with saidrotor and said rotor winding; a magnet c compass; a sec-- ond rotorcoupled to said magnetic compass and oriented thereby in-correspondencewith thedirectional position thereof; a second rotor windingmagnetically coupled to said second rotor; .a sec- 0nd stator winding ininductive relation with said second rotor and said second rotor winding,said stator windings being symmetrically interconnected electrically; asource of alternating current in circuit connection with one of saidtheir predetermined directional alignment for inducing a correctiveprecessional action on said gyroscope to restoresaid alignment.

2. A compass system comprising a gyroscope; a first rotor coupled tosaid gyroscope and oriented thereby in correspondence with thedirectional position thereof; a first rotor winding magnetically coupledto said rotor; a first multiphase stator winding in inductive relationwith said first rotor andsaid first rotor winding; a magnetic compass; asecond rotor coupled to said magnetic compass and oriented thereby incorrespondence with the directional position thereof a second rotorwinding'magneti-cally coupled to saidsecond rotor; a second multi-phasestator winding in inductive relation with said second rotor and saidsecond rotor winding, said stator windings being symmetricallyinterconnected electrically; a source of single phase alternatingcurrent in circuit connection with one of said rotor windings; and meansresponsive to signals received by the other of said rotor windings fromits associated stator winding when the gyroscope and the magneticcompass are out of their predetermined directional alignment forinducing a corrective precessional action on said gyroscope to restoresaid alignment.

3. A compass system comprising a gyroscope; a first rotor coupled tosaid gyroscope and oriented thereby in correspondence with thedirectional position thereof; a first rotor winding magnetically coupledto said rotor; a. first stator winding coupled to said magnetic compassand oriented thereby in correspondence with the directional,

position thereof; a second rotor winding magnetically coupled to saidsecond rotor; a second stator winding in inductive relation with saidsecond rotor and said second rotor winding, said stator windings beingsymmetrically interconnected electrically; a source of alternatingcurrent in circuit connection with one of said rotor windings; andelectronic means responsive to sig. nals received by the other of saidrotor windings from its associated stator winding when the gyroscope andthe magnetic compass are out of their predetermined directionalalignment for inducing a corrective precessional action on saidgyroscope to restore said alignment. 1

4. A compass system comprising a directional gyroscope; a first rotorcoupled to saididirectio'nal gyroscope and oriented thereby incorrespondence with the directional position thereof; a first rotorwinding magnetically coupled to said first rotor; a first stator windingin inductive relation with said first rotor and said first rotorwinding; a magnetic compass; a second rotor coupled to said magneticcompass and oriented thereby in correspondence with the directionalposition thereof; a second rotor winding magnetically coupled to saidsecond rotor; a second stator winding in inductive relation with saidsecond rotor and said second rotor winding, said stator windsecured tothe horizontal gimbal ring of the gyroscope and coil means adjacent saidring; and 1 means responsive to signals received by said second rotorwinding when the gyroscope and the magnetic compass are .out oi theirpredetermined directional alignment for inducing a correctiveprecesional action on said gyroscope comprising an electronic amplifierconnected to said cfiil 2:

means for creating a unidirectional magnetic fi about said magnet bar.

5. A compass system comprising a directional gyroscope; a first pick-offunit having a rotor pick-oil unit; means for altering the directionalorientation of said gyroscope including a magnet bar secured to thehorizontal gimbal ring of the gyroscope and two coils adjacent saidring; and

means responsive to signals received by said sec-- ond pick-ofl unitfrom said first pick-oil unit when the directional gyroscope and themagnetic compass are out of their predetermined directional alignmentfor inducing a corrective precessional action on saiddirectionalgyroscope comprising an electronic amplifier and a pair of spacedischarge devices operatively'associated with said electronic amplifierand each connected to one of said coils for creating a unidirectionalmagnetic flux about said magnet bar in the proper sense to efiect therestoration. i

6. A compass system comprising a directional gyroscope; a first pick-oilunit having a rotor coupled to said directional gyroscope and orientedthereby in correspondence with the directional position thereof; a manetic compass; a second pick-oil unit having a rotor coupled to said magnetic compass and oriented thereby in correspondencewith the directionalposition thereof; circuit means electrically interconnecting saidpick-off units; a source of single phase alternating current in circuitconnection with said first pick-off unit; means for altering thedirectional orientation of said gyroscope includinga magnet bar securedto the horizontal gimbal ring of the gyroscope and two coils adjacentsaid ring; means responsive to signals received by said second. pickoffunit from said first pick-oil imit when the directional gyroscope andthe magnetic compass are out or their predetermined directionalalignment for inducing a corrective precessional action on saiddirectional gyroscope comprising an electronic amplifier and a pair ofspace discharge devices operatively associated with said electronicamplifier and each connected to one of said coils for creating aunidirectional magnetic fiux about said magnet bar in the proper senseto effect the restoration; and mechanism connected in series with saidcoils and said spac discharge devices for adjusting th rate of saidcorrective precessiona action on said gyroscope.

7. compass system comprising a directional gyroscope; a first pick-offunit having a rotor coupled to said directional gyroscope and orientedthereby in correspondence with the directional position thereof; amagnetic compass; a second pick-ofi unit having a rotor coupled to saidmagnetic compass and oriented thereby in correspondence with thedirectional position thereof;

ing current circuit connection with said first pick-off unit means foraltering the directional orientation of said gyroscope including amagnet bar secured to the horizontal gimbal ring of the gyroscope andtwo coils adjacent saidring; and means responsive to signals received bysaid second pick-ofi'unit from said first pick-off unit when thedirectional gyroscope and the magnetic compass are out of theirpredetermined directional alignment for inducing a correctiveprecessional action on said directional gyroscope comprising anelectronic amplifier and a pair of space discharge devices operativelyassociated with said electronic amplifier and each connected to one ofsaid coils for creating a unidirectional magnetic flux about said magnetbar in the proper sense to effect the restoration; and means for testingand adjusting the sensitivity of said space discharge devices.

8. Acompass system comprising a directional gyroscope; a first pick-oilunit having a rotor coupled' to'isaid directional gyroscope and orientedthereb'yi in correspondence with the directional position thereof; amagnetic compass; a second pick-off unit having a rotor coupled to saidmagnetic compass and oriented thereby in correspondence with thedirectional position thereof; circuit means electrically interconnectingsaid pick-of! units; a source of singl phase alternating current incircuit connection with said first pick-off unit; means for altering thedirectional orientation of said gyroscope including a magnet bar securedto the horizontal gimbal ring of the gyroscope and two coils adjacentsaid ring; and means responsive to signals received by said secondpick-01f unit from said first pick-off unit when the directionalgyroscope and the magnetic compass are out of their predetermineddirectional alignment for inducing a corrective precessional action onsaid directional gyroscope comprising an electronic amplifier and a pairof space discharge devices operatively associated with said electronicamplifier and each connected to one of said coils for creating aunidirectional magnetic flux about said magnet bar in the proper senseto effect the restoration; mechanism connected in series with said coilsand said space discharge devices for adjusting the rate of saidcorrective precessional action on said gyroscope; and means for testingand adjusting the sensitivity of said space discharge devices.

9. A compass system comprising a gyroscope; a first rotor coupled tosaid gyroscope and oriented thereby in correspondence with thedirectional position thereof; a first rotor winding magnetically coupledto said rotor; a first stator-winding in inductive relation with saidrotor and said rotor winding; a magnetic compass; a second rotor coupledto said magnetic compass and oriented thereby in correspondence with thedirectional position thereof; a second rotor winding magneticallycoupled to said second rotor; a second stator winding in inductiverelation with said second rotor and said second rotor winding; saidstator windings being symmetrically interconnected electrica y; a sourceof alternating current in circuit connection with .one of said rotorwindings; and mans connected to said source of alternating currentand'responsive to signals received by the other of'said rotor windingsfrom its associated stator winding. when the gyroscope and the magneticcompass are out of ther predetermined directional alignmentfor'incircuit means electrically interconnecting said pick-oft units; asource of single phase alternatducing a corrective precessional actionon said gyroscope to restore said alignment.

10. A compass system comprising a gyroscope; a first rotor coupled tosaid gyroscope and oriented thereby in correspondence with thedirectional position thereof; a first rotor winding magneticall coupledto said first rotor; a first multiphase stator winding in inductiverelation with said first rotor and said first rotor winding; a

magnetic compass; a second rotor coupled to said magnetic compass andoriented thereby in correspondence with the directional positionthereof; a; second rotor winding magnetically coupled to'said "secondrotor; a second multiphase stator winding in inductive relation withsaid second rotor and said second rotor winding; said stator windingsbeing symmetrically interconnected electrically; a source of singlephase alternating current in circuit connection with one of said rotorwindings; and electronic means connected to said source ofalternatingcurrent and responsive to alternating current signals impressed uponsaid second rotor winding by said second stator winding when thegyroscope and the m88 netic compass are out of their predetermineddirectional alignment for inducing a corrective precessional action onsaid gyroscope to restore said alignment.

11. A compass system comprising a gyroscope; a first pick-oil unithaving a rotor coupled to said gyroscope and oriented thereby incorrespondence With'the directional position thereof; a magneticcompass; a second pick-oil unit having a rotor coupled to said magneticcompass and oriented thereby in correspondence with the directionalposition thereof; circuit, means electrically interconnecting saidpick-off units; a source of alternating current in circuit connectionwith said first pick-oifunit; means for altering the directionalorientation of said gyroscope including a magnet bar secured to thehorizontal gimbal ring of the gyroscope and two coils adjacent saidring'and connected to saidsource of alternating current; an electronicamplifier having a grid connected to said second pick-off unit; a pairof grid-controlled space discharge devices operatively associated withsaid electronic amplifier; a pair of adjustable resistances eachconnected to one of said space discharge devices and to one of saidcoils; means responsive to signals received by said second pickofl unitfrom said first pick-ofi unit when the gyroscope and magnetic compass arout of their predetermined directional alignment for impressing apotential upon the grid of said electronic amplifier to selectivelyrender effective said space discharge devices for energizing one of saidcoils for inducing a corrective precessional action on said gyroscope torestore said alignment; and circuit means for impressing a negativepotential derived from the cathode of one of said space dischargedevices upon the grid of the other of said space discharge devices; saidadjustable resistances being effective to adjust the rate of saidcorrective precessional action.

12. A compass system comprising a gyroscope; a first pick-oil unithaving a rotor coupled to said gyroscope and oriented thereby incorrespondence with'the directional position thereof; a magneticcompass; a second pick-off unit having a rotor coupled to said magneticcompass and oriented thereby in correspondence with the directionalposition thereof; circuit means electrically interconnecting saidpick-ofl units; a source of alternating current in circuitconnectionwith said first pick-oi! unit; means for altering the directionalorientation of said gyroscope including a magnet bar secured to thehorizontal gimbal ring of the gyroscope and two coils adjacent said ringand connected to said source of alternating current; an electronicamplifier having a grid connected to saidsecond pick-of! unit; a pair ofgridcontrolled space discharge devices operatively associated with saidelectronic amplifier; a pair of adjustable resistances each connected toone of said space discharge devices and to one of said coils; meansresponsive to signals received by said second pick-off unit from saidfirst pick-oil unit when the gyroscope and ma netic compass are out oftheir predetermined directional alignment for impressing a potentialupon the grid 01' said electronic. amplifier to selectively rendereffective said space discharge devices for energizing one of said coilsfor inducing a corrective precessional action on said gyroscope torestore said alignment; circuit means for impressing a negativepotential derived from the cathode of one of said space dischargedevices upon the grid of theother of said space dischargedevices; andcircuit means for impressing a portion of saidnegative potential uponthe grid of said on space discharge device; said adjustable resistancesbeing effective of said corrective 'precessional' with the directionalposition thereof; a magnetic" compass; a second pick-ofi unit having arotor coupled to said magnetic compass and oriented thereby incorrespondence with the directional position thereof; circuit meanselectrically interconnecting said pick-ofl units; a source ofalternating current in circuit connection with said first pick-ofi unit;means for altering the directional orientation of said gyroscopeincluding a magnet bar secured to the horizontal gimbal rin of thegyroscope and two coils adjacent said ring and connected to said sourseof alternating current; an electronic amplifier having a grid connectedto said second pick-oi! unit; a pair of gridcontrolled space dischargedevices operatively associated with said electronic amplifier; a pair ofsecured to the horizontal gimbal ring of the gyroscope and two coilsadjacent saidring and connected to said source of alternating current; a

cascade amplifier having a grid connected to said second pick-of! unitand a pair of plates; an inverse feed back circuit interconnecting saidplates;

a pair ofspace discharge devices each connected vices to said cascadeamplifier; and means responsive to signals received by said secondpickofl unit from said first pick-off unit when the gyroscope andmagnetic compass are out of their ---predetermined directional alignmentfor impressing an alternating potential derived from said sourceoralternating current upon the grid of said cascade amplifier toselectively render effective said space discharge devices for energizingone of-said' coils to induce-a corrective precessional action on saidgyroscope to restore said' alignment." v v 15. A compass systemcomprising a gyroscope; a first pick-oil unit having a rotor coupled tosaid gyroscope andoriented thereby in accordance adjustable resistanceseach connected to one of said space discharge devices and to one of saidcoils; means responsive to signals received bysaid second pick-oi! unitirom said first pick-cit unit when the gyroscope and magnetic compassare out of their predetermined directional alignment for impressing apotential upon the grid 01 said electronic amplifier. to selectivelyrender efiective said space discharge devices for energizing one of saidcoils for inducing a corrective precessional action on said gyroscope torestore said alignment; circuit means for impressing a negativepotential derived from the cathode of. one of said space dischargedevices upon th grid of the other or said space discharge devices;circuit -means for impressing a portion or said negative potential uponthe grid of said one space discharge device: and mechanism connected inseries with the cathodes or said space discharge devices for testing andsetting the sensitivity thereof; said adjustable resistances beingeffective to adjust the rate of said corrective precessional action.

14. A compass system comprising a gyroscope; a first pick-oi! unithaving a rotor coupled to said gyroscope and oriented thereby inaccordance with the directional position thereof; a magnetic compass; asecond pick-off unit having a rotor concompass; asecond pick-oil .unithaving a .rotor coupled to said magnetic compass and oriented thereby inaccordance with the directional position thereof; circuit meanselectrically interconconnecting said pick-off units; a source ofalternating current. in circuit connection with said first pick-oi!unit; means for altering the directional orientation of said gyroscopeincluding a magnet bar secured to the horizontal gimbal ring of thegyroscope and two coils adjacent said ring and connected to said sourceof alternating current; an electronic amplifier having a grid connectedto said second pick-ofl unit; a pair of space discharge devices; circuitmeans connecting the grids of said space. discharge devices to saidelectronic amplifier; a pair of resistance banks each connected to oneor said space discharge devices; a gang switch having a pair of contactarms each adjustably associated with one of said resistance banks andeach connected to one of said coils; and means responsive to signalsreceived by said second pick-oft unit from said first pickoff unit whenthe gyroscope and magnetic compass are out of their predetermineddirectional alignment for impressing an alternating potential derivedfrom said source of alternating current upon the grid of said electronicamplifier to selectively render effective said space discharge devicesfor energizing one of said coils to induce a corrective precessionalaction on said gyroscope to restore said alignment, said resistancebanks and gang switch being effective to adjust the rate of saidcorrective precessional action.

16. A compass system comprising a gyroscope; a first pick-oil unithaving a rotor coupled to said gyroscope and oriented thereby inaccordance with the directional position thereof; a

magnetic compass; a second pick-oi! unit having. a rotor coupled to saidmagnetic compass and oriented thereby in accordance with the directionalposition thereoij; circuit means electrically, interconnecting saidpick-ofl units; a source oi alternating current in circuit connecinseries with one of said coils; circuit means connecting the grids ofsaid space discharge dewith the directional position thereof; a magnetiction with said first pick-oil! unit; means for altering the directionalorientation of said gyroscope including a magnet bar secured to thehorizontal gimbal ring of the gyroscope and two coils adjacent said ringand connected to said source of alternating current; an electronic am-Dlifier having a grid connected to said second pick-oi! unit; a pair ofspace discharge devices each connected in series with one 01' saidcoils;

circuit means connecting the grids of said space discharge devices tosaid electronic amplifier; means responsive to signals received by saidsecond pick-on unit from said first pick-oi! unit when the gyroscope andmagnetic compass are out of their predetermined directional alignmentfor impressing an alternating potential derived irom said source ofalternating current upon the grid of said electronic amplifier toselectively render eil'ective said space discharge devices forenergizing one or said coils to induce a corrective precessional actionvon said gyroscope to restore said alignment; and adjustable impedancemeans tor varying the grid bias of said space discharge devices tocontrol the sensitivity or said corrective precessional action.

17. A compass system comprising a gyroscope; a first pick-oil unithaving a rotor coupled to said gyroscope and oriented thereby inaccordance with the directional position thereof; a

magnetic compass; a second pick-oi! unit having a rotor coupled to saidmagnetic compass and oriented thereby in accordance with the directionalposition thereof; circuit means electrically interconnecting saidpick-oi! units; a source oi -alternating current in circuit connectionwith said first pick-oi! unit; means for altering the directionalorientation of said gyroscope including a magnet bar secured to thehorizontal gimbal ring 01 the gyroscope and the coils adjacent said ringand connected to said source of alternating current; an electronicamplifier having a grid connected to said second pick-on unit; a pair ofspace discharge devices; circuit means connecting the grids of saidspace discharge devices to said electronic amplifier; a pair ofadjustable resistances each connected to one or said space dischargedevices and to one of said coils; means responsive to signals receivedby saidsecond pick-oi! unit from said firsfipickwd unit when thegyroscope and magnetic compass are out of their predetermineddirectional alignment for impressing an alternating potential derivedfrom said source of alternating current upon the grid of said electronicamplifier to selectively render eflective said space discharge devicesfor energizing one of said coils to induce a corrective precessionalaction on said gyroscope to restore said alignment; and adjustableimpedance means for varying the grid bias of said space dischargedevices to control the sensitivity of said corrective precessionalaction; said adjustabl resistances being eflective to adjust the rate ofsaid corrective precessional action.

18. Acompass system comprising a gyroscope; a first pick-oi! unit havinga rotor coupled to said gyroscope and oriented thereby in accordancewith the directional position thereof; a magnetic compass; a secondpick-oil unit having a rotor-coupled to said magnetic compass andoriented thereby in accordance with the directional position thereof;circuit means electrically interconnecting said pick-oil units; a sourceoi. alternating current in circuit connection with said first pick-ctrunit; means for altering the directional orientation of said gyroscopeincluding a magnet bar secured to the horizontal elm connecting thegridsof said space discharge devices to said electronic amplifier; apair of adjustable resistances each connected to one of said spacedischarge devices and to one of said coils; means responsive to signalsreceived by said second pick-oi! unit ,i'rom said first pickoi! unitwhen the gyroscope and magnetic compass are out of their predetermineddirectional alignment for impressing an alternating potential derivedfrom said source of alternating current upon the grid of saidelectronicamplifier to selectively render efi'ective said space discharge devicesfor energizing one or said coils to induce a corrective precessionalaction on said gyroscope to restore said alignment; adjustableimpedancemeans for varying the grid bias of said space discharge devicesto control the sensitivity of said corrective precessional action; and apair of jack means each connected in series with the cathode of one ofsaid space discharge devices whereby impedances may be connected inseries with said cathodes to determine the proper setting of saidadjustable impedance means; said adjustable resistances being eii'ectiveto adjust the rate of said corrective pre'cessional action.

19. A compass system comprising a gyroscope;

a first pick-oi! unit having a rotor coupled to said gyroscope andoriented thereby in accordance with the directional position thereof; amagnetic compass; a second pick-oil unit having a rotor coupled to saidmagnetic compass and oriented thereby in accordance with the directionalposition thereof; circuit means electrically interconnecting saidpick-oil. units; a source of alternating current in circuit connectionwith said first pick-oil unit to impress an alternatin potentialthereon; means for altering the directional orientation of saidgyroscope including a magnet bar secured to the horizontal gimbal ringoi'the gyroscope and twocoils adjacent said ring and connected to. saidsource of alternating current; an electronic amplifier having a gridconnected to said second pick-on unit; a pair of space discharge deviceseach connected in series with one of said coils; circuit meansconnecting the grids 01' said space discharge devices to said electronicamplifier; means responsive to signals received by said second pick-oil!unit from said first pick-of! unit when the gyroscope and magneticcompass are out. of their predetermined directional alignment forimpressing an alternating potential derived from said source oialternating current upon the grid oi. said electronic amplifier toselectively render efi'ective said space discharge devices forenergizing one or said coils to induce a corrective precessionai actionon said gyroscope to restore said alignment; and means for preselectingthe phase relation of the alternating potential impressed on said firstpick-oi! unit with respect to the alternating potential of said sourceoi alternating current. a

' WIILIAM P. LEAR.

